Headlights dim at random times and now I've noticed at the same time the heater fan power decreases. I've had the vehicle jumped twice in the past three months before I purchased a new battery. Is this an electrical problem, or alternator, or a relay?
It sounds like the alternator is going bad. When the lights dim, check the alt gauge to see if it is low. With the engine running, it should be producing around 14 volts. With the engine off, it will drop to around 12v.